Unforeseen Limitations to Classful Addressing

The original Internet designers never envisioned that the Internet

would grow into what it has become today. Many of the problems that

the Internet is facing today can be traced back to the early decisions

that were made during its formative years.

  During the early days of the Internet, the seemingly unlimited

address space allowed IP addresses to be allocated to an organization

based on its request rather than its actual need. As a result, addresses

were freely assigned to those who asked for them without concerns

about the eventual depletion of the IP address space.

  The decision to standardize on a 32 bit address space meant that there

were only 232 (4,294,967,296) IPv4 addresses available. A decision to

support a slightly larger address space would have exponentially

increased the number of addresses thus eliminating the current

address shortage problem.

  The classful A, B, and C octet boundaries were easy to understand

and implement, but they did not foster the efficient allocation of a

finite address space. Problems resulted from the lack of a network

class that was designed to support medium sized organizations. For

example, a /24, which supports 254 hosts, is too small while a /16,

which supports 65,534 hosts, is too large. In the past, sites with sev 

eral hundred hosts were assigned a single /16 address instead of two

/24 addresses. This resulted in a premature depletion of the /16 net 

work address space. Now the only readily available addresses for

medium sized organizations are /24s, which have the potentially nega 

tive impact of increasing the size of the global Internet's routing table.

Figure 6 shows basic class A, B, and C networks. 

U N D E R S TA N D I N G   I P   A D D R E S S I N G

6